1. Field
The disclosure relates to filter design, and in particular, to the design of current-mode low-pass filters.
2. Background
In the art of filter design, a current-mode filter may be used to filter a signal in the current domain. Such current-mode filters are advantageously employed in applications wherein, e.g., a preceding and/or subsequent circuit block processes signal currents, as opposed to signal voltages. For example, in a communications transmitter application, the output of a digital-to-analog converter (DAC) and the input to an up-conversion mixer are both commonly designed to process signal currents, and thus a current-mode filter may be readily employed between the DAC and the mixer to, e.g., low-pass filter the DAC output current prior to providing to the mixer input.
Certain prior art current-mode filters employ a current mirror topology, wherein one or more resistor-capacitor (RC) networks are coupled between the gates of the current mirror transistors to provide low-pass filtering. While being conceptually simple to design and implement, such prior art designs exhibit certain disadvantages, in particular, a generally low quality factor (Q) that is limited to at most ½. It will be appreciated that filters for, e.g., communications transceivers, will in general require higher Q's to achieve a desired attenuation at a given frequency while minimizing in-band attenuation.
It would be desirable to provide novel techniques for designing a current-mode filter with arbitrarily high Q, and furthermore having a natural frequency that may be arbitrarily selected.